The present invention is directed to manufacturing apparatus and methods, and more specifically, to apparatus and methods for fabricating a helicopter main rotor blade.
There is a growing trend in the aerospace industry to expand the use of composite materials for a diverse array of structural and dynamic applications. One particular application for the use of composite materials lies in the fabrication of main rotor blades for helicopters.
With increased usage of composite materials to fabricate main rotor blades, the helicopter industry is continually seeking to improve the tooling and/or methods used to fabricate main rotor blades so as to reduce the per unit fabrication costs associated with the main rotor blades. Typically, the per blade fabrication costs are higher than need be due to part rejections or rework that occurs during the main rotor blade fabrication process. Part rejections typically occur where the composite material has been so substantially damaged during the fabrication process that rework is not cost effective or where a finished fabricated part exceeds the tolerance limits established for the part. Rework occurs where the composite material has been damaged during the fabrication process, and the damage may be repaired in a relatively cost effective manner.
Sikorsky Aircraft has developed a parallel manufacturing protocol for fabricating helicopter main rotor blades wherein a blade subassembly and a leading-edge sheath are concurrently fabricated as individual components, and then the prefabricated blade subassembly and the prefabricated leading-edge sheath are integrated in combination to form an assembled main rotor blade. The assembled main rotor blade is subsequently cured to form a finished main rotor blade. This protocol was adopted in large measure because experience has shown that the leading edges of main rotor blades are subjected to varying degrees of abrasion during helicopter operations. As a result of such abrasion effects, the leading edge of a helicopter main rotor blade at some point becomes aerodynamically unsuitable for further use. Rather than replacing the entire main rotor blade, it was determined that a replaceable leading-edge sheath would allow abrasion-degraded main rotor blades to be efficaciously and economically repaired.
The prior art process for fabricating blade subassemblies involved the use of a xe2x80x9cclamshellxe2x80x9d tooling fixture and a xe2x80x9cwetxe2x80x9d lay-up process for the composite materials. It was determined that the rejection rate for blade subassemblies fabricated using the clamshell tooling fixture and the wet lay-up process was unacceptable in light of the today""s competitive market. The dependability and accuracy of the clamshell tooling fixture depended upon the stability of the laid up tooling contours, the proper securing and pinning of all fasteners and locators, and the variability in applying blade outer mold line pressures. The clamshell tooling fixture and the wet lay-up process were subjected to shrinkage and lose of tolerances, which led to component rejection. The clamshell configuration result in asymmetrical pressure distributions across the layed-up blade subassembly.
Another area of concern in the parallel manufacturing protocol was the sheath spreader tool used to integrate the leading-edge sheath in combination with the blade subassembly. The leading-edge sheath has a prefabricated configuration that does not allow the sheath to be inserted directly onto the blade subassembly. Rather, the aft edges of the leading-edge sheath must be spread apart to allow the leading-edge sheath to be inserted onto the blade subassembly. The prior art sheath spreader tool comprises segmented angular stainless steel sheet metal grabbers that are mounted spanwise on the aft edges of the leading-edge sheath in contact with the inner mold line (IML) surfaces (which are formed of composite material) of the leading-edge sheath. Each segment of the prior art grabber is individually actuated by means of a side cam lever. The prior grabbers exert a shearing action against the IML surfaces of the leading-edge sheath in spreading the aft edges of the sheath apart. The shearing action caused by the prior art grabbers caused cracks and delaminations in the composite material subjected to the shearing action thereof, resulting in component rejections or rework. In addition to the foregoing deficiency of the prior art leading-edge sheath spreader tool, the segments of the grabber are individually actuated in a sequential manner such that to spread apart the entire leading-edge sheath involves multiple, repetitive operations. Not only is such a procedure labor intensive and time consuming, and hence costly, such a procedure may induce unwanted stresses into the aft edges of the leading-edge sheath.
A need exists to provide an apparatus for spreading a leading-edge sheath for insertion onto a blade subassembly without inducing cracks and/or delaminations in the composite material of the leading-edge sheath. Preferably, the apparatus should spread the leading-edge sheath apart in a single operation to reduce the time required to spread the leading-edge sheath apart. A need also exists to provide a fixture for assemblage and compacting of a blade subassembly that provides a uniform pressure distribution during the compaction of the blade subassembly, that facilitates the use of prepreg composite materials, and that ensures proper chordwise and spanwise alignment of the components of the blade subassembly layed-up in the fixture. A need also exists to provide a sheath spreading apparatus and compaction fixture which in combination simplify the insertion of a spread-apart leading-edge sheath onto the blade subassembly.
One object of the present invention is to provide a sheath spreading/insertion apparatus that spreads apart a leading-edge sheath without inducing cracks and/or delaminations in the composite material thereof.
Another object of the present invention is to provide a sheath spreading/insertion apparatus that spreads apart a leading-edge sheath in a single operation.
A further object of the present invention is to provide a compaction fixture for assemblage and compaction of blade subassembly components that provides a uniform pressure distribution during compaction of the blade subassembly.
Still another object of the present invention is to provide a compaction fixture that ensures proper chordwise and spanwise alignment of the components comprising the blade subassembly as assembled in the compaction fixture.
One more object of the present invention is to provide a sheath spreading/insertion  positioning apparatus and a compaction fixture which, in combination, greatly simplify the insertion  of a spread-apart leading-edge sheath assembly onto  in relation to the blade subassembly.
These and other objects of the present invention are achieved by a sheath spreading/insertion  positioning apparatus according to present invention for spreading a leading-edge sheath and inserting  positioning the spread-apart leading-edge sheath in combination with  relation to a blade subassembly. The sheath spreading/insertion  positioning apparatus comprises a movable  stanchion, an upper  a first elongate carriage member mounted in movable combination with the movable  stanchion and a lower  second elongate carriage member mounted in movable combination with the movable  stanchion. A plurality of suction cups are mounted in combination with each of the upper  first and lower  second elongate carriage members. A means is provided by imparting synchronized movement to the upper  first and lower  second carriage members between a disengaged position wherein the leading-edge sheath may be inserted between the pluralities of suction cups mounted in combination with the upper  first and lower  second carriages without contact therewith, an engaged position wherein the pluralities of suction cups abuttingly engage respective outer mold line (OML) surfaces of the leading-edge sheath, and an operating position wherein the leading-edge sheath is spread apart for insertion onto  positioning in relation to the blade subassembly. A means is provided for generating suction forces in the pluralities of suction cups in the engaged position to cause the suction cups to hold the respective OML surfaces of the leading-edge sheath such that subsequent synchronized movement of the upper  first and lower  second carriage members to the operating position causes the leading-edge sheath to be spread apart. A means is provided for moving the movable stanchion  imparting relative movement between the spread-apart leading-edge sheath and the blade subassembly to insert  position the spread-apart leading-edge sheath onto  in relation to the blade subassembly.
The sheath spreading/insertion  positioning apparatus further includes a means for indicating that the spread-apart leading-edge sheath has been fully inserted onto  positioned in relation to the blade subassembly. The synchronized movement imparting means comprises a plurality of pneumatic cylinders mounted in combination with the upper  first elongate carriage member and the movable  stanchion, a plurality of pneumatic cylinders mounted in combination with the lower  second elongate carriage members and the movable  stanchion, and a pressure source pneumatically interconnected to the pluralities of pneumatic cylinders. Actuation of the pressure source provides pressurized air to the pluralities of pneumatic cylinders to cause synchronized movement of the upper  first and lower  second elongate carriage members between the disengaged position wherein the leading-edge sheath may be inserted between the pluralities of suction cups mounted in combination with the upper  first and lower  second elongate carriage members without contact therewith, the engaged position wherein the pluralities of suction cups abuttingly engage respective OML surfaces of the leading-edge sheath, and the operating position wherein the leading-edge sheath is spread apart for insertion onto  positioning in relation to the blade subassembly. For the described embodiment, ninety suction cups are mounted in combination with the upper  first elongate carrier member and ninety suction cups are mounted in combination with the lower  second elongate carrier member.
To spread and insert  position the leading-edge sheath in combination with  relation to a blade subassembly, the leading-edge sheath is mounted between upper  first and lower  second rows of suction cups, the upper  first and lower  second rows of suction cups are displaced in synchronized movement to an engaged position wherein the suction cups abuttingly engage respective OML surfaces of the leading-edge sheath, suction forces are generated in the upper  first and lower  second rows of suction cups to cause the suction cups to hold the respective OML surfaces of the leading-edge sheath, the upper  first and lower  second rows of suction cups are displaced in synchronized movement to an operating position to cause the leading-edge sheath to be spread apart, and the spread-apart leading-edge sheath is inserted onto  positioned in relation to the blade subassembly.
A compaction fixture according to the present invention is provided for assembling and compacting a blade subassembly that includes upper and lower composite skins, a honeycomb core, and a spar assembly (a spar with at least one counterweight bonded thereto). The compaction fixture comprises a lower assembly that includes a support structure and a contoured upper airfoil nest mounted in combination with the support structure. The contoured upper airfoil nest has an OML surface that defines the airfoil surface of the upper composite skin, a plurality of tooling pins for locating the upper composite skin, honeycomb core combination in the contoured upper airfoil nest, and a plurality of pusher pins for locating the spar assembly in chordwise alignment in the contoured upper airfoil nest. A spar stanchion is mounted in combination with the inboard and outboard ends of the contoured upper airfoil nest, respectively, for locating the spar assembly in spanwise alignment in the contoured upper airfoil nest. The compaction fixture further comprises an upper assembly that includes a structural support truss, a contoured backplate affixed to the structural support truss, and a pressure bag having chordwise and spanwise dimensions corresponding to the blade subassembly fastened in sealed combination with the contoured backplate. A means is provided for locking the upper and lower assemblies in combination so that compaction of the blade subassembly assembled in the lower assembly may be effectuated. A means is provided for pressurizing the pressure bag to compact the blade subassembly disposed in the locked upper and lower assemblies. The compaction fixture may further include a caul plate interposed between the upper and lower assemblies to provide uniform pressure distribution over the layed-up blade subassembly during compaction thereof.
To assemble and compact the blade subassembly, a composite fixture as described in the preceding paragraph is provided. The upper composite skin and the honeycomb core are layed-up in combination in the contoured upper airfoil nest. The spar assembly is located in chordwise and spanwise alignment in the contoured upper airfoil nest, and the lower composite skill is layed-up in combination with the spar assembly and the honeycomb core. The upper and lower assemblies are locked in combination and the pressure bag is pressurized to compact the assembled blade subassembly.